In recent years, as a printing plate for off-set printing, a large number of computer to plate (CTP) systems have been developed and put into practical use, which imagewise exposes directly to a planographic printing plate material employing laser light based on digital image data to record an image on the material.
Among them, in a printing plate making field in which a fairly high printing durability is required, it is known a negative type planographic printing plate material having a photosensitive layer containing a polymerizable compound.
Proposed as polymerization initiators employed in a polymerizable photosensitive layer are s-triazine compounds having a trichloromethyl group described, for example, in Japanese Patent Publication Open to Public Inspection hereinafter refereed to as JP-A) Nos. 48-36281, 54-74887, and 64-35548, iron arene complexes and peroxides described, for example, in JP-A No. 59-219307, monoalkyltriaryl borates described, for example, in JP-A Nos. 62-150242, 62-143044, and 64-35548, titanocene compounds described, for example, in JP-A Nos. 63-41483 and 2-291.
However, the photographic speed of photosensitive lithographic printing materials having a photosensitive layer employing these polymerization initiators has been insufficient and an increase has been sought.
Further, a technique has been proposed in which a tertiary amino group is introduced into the structure of compounds containing a polymerizable ethylenic double bond, and trihalogenated methyl-s-triazine compounds are simultaneously employed as a polymerization initiator. This technique has resulted in an increase in photographic speed, while the resulting length-of-run capacity was insufficient (refer to Patent Document 1).
In addition, a technique has been proposed in which a tertiary amino group is introduced into the structure of ethylenic double bond containing compounds, and trihalogenated methyl-s-triazine compounds are incorporated as a polymerization initiator, and further metallocene compounds such as titanocenes are simultaneously employed. This technique resulted in an increase in photographic speed, however the resulting length-of-run capacity was still insufficient (refer to Patent Document 2).
(Patent Document 1) JP-A No. 1-105238
(Patent Document 1) JP-A No. 2-127404